A book that gets into the mind of a narcissist or a liar or a cheater.

I've always wondered what "bad" people think when they are alone in bed at night. How they think of themselves and what are the excuses they give themselves to keep going.
I thought the best way to know is to read a book/novel about that. I don't want an educational book.
Thriller and psychological books are my fav. But could be drama or anything light too.
(I lean towards more dark tragic heavy close to harsh hidden reality books)

Edit: THANK YOU GUYS THIS SUMMER IS GONNA BE EXCITING!